The present invention relates to an exposure method, a mask data producing method, and a semiconductor device manufacturing method.
Recently, with a finer design rule of a semiconductor device, fine dimensional control is required in a lithography process for patterning a device pattern. In order to secure the fine dimensional control, even if a position of a processed substrate has a slight error with respect to an ideal position at which a photoresist is placed at a focal position of a mask pattern image in exposing the mask pattern image onto the photoresist applied to the processed substrate, it is necessary that an error allowable range of the focal position be sufficiently ensured such that the dimensions of the photoresist formed after the patterning falls within the allowable range, that is, it is necessary to sufficiently ensure a focal depth.
Further, even if an exposure amount that should be given to the photoresist has a slight error with respect to an ideal value in exposing the mask pattern image onto the photoresist applied to the processed substrate, it is necessary that an error allowable range of the exposure amount be sufficiently ensured such that the dimensions of the photoresist formed after the patterning falls within the allowable range, that is, it is necessary to sufficiently ensure a margin of the exposure amount.
However, when the exposure is actually performed to check the dimensions of the photoresist after the patterning, unfortunately the dimensional control is lowered to lower a production yield of a semiconductor device although best focus positions of a dense pattern and an isolated pattern are designed so as to be optically matched with each other. The lowering of the dimensional control is caused by a loss of the focal depth and lowering of the margin of the exposure amount. The loss of the focal depth is generated due to a mismatch between the best focus positions of the dense pattern and isolated pattern, that is, the presence of so-called sparse and dense best focus difference (hereinafter appropriately referred to as “inter-pattern best focus difference” in the broad sense). The margin of the exposure amount is lowered by an influence of a standing wave that is generated in the photoresist by interference between exposure light incident to the photoresist and exposure light reflected at an interface on a lower side of the photoresist.
In order to deal with the problem, for example, Japanese patent Application Laid-Open No. 2004-103674 proposes a technique of improving a production yield of a semiconductor integrated circuit. In the technique proposed in Japanese patent Application Laid-Open No. 2004-103674, in consideration of factors such as a focus, an exposure amount, a mask pattern shape, and a difference between pieces of exposure apparatus (such as aberration) which affect the dimension of the transferred pattern, a response model is produced by evaluating dependence of a response of an exposure condition such as a best focus shift on the pattern, and the exposure condition is previously corrected to improve the production yield.
In the technique proposed in Japanese patent Application Laid-Open No. 2004-103674, it is expected that the lowering of the yield can be restrained to the minimum level by optimizing the controllable exposure condition even if the dimensional control is lowered. It is also expected that the sparse and dense best focus difference is reduced by optimizing the exposure condition. However, a time and cost necessary to produce the response model become troublesome, and the technique proposed in Japanese patent Application Laid-Open No. 2004-103674 is hardly introduced as a direct method for restraining the generation of the sparse and dense best focus difference.
In another technique disclosed in Japanese patent Application Laid-Open No. 2006-73709, in order to avoid the lowering of the margin of the exposure amount caused by the standing wave generated by the interference of the exposure light in the photoresist, a multilayer antireflection film in which reflectivity of the exposure light is equal to or lower than 0.5% is formed between the photoresist layer and the processed film to restrain the standing wave effect.
It is noted that generally the reflectivity depends on an incident angle. Generally, the incident angle to the photoresist of the light relating to the image formation in the exposure light is increased with a finer device pattern. Even if a desired antireflection performance is obtained in a certain device pattern, frequently the desired antireflection performance is not obtained when the device pattern is shrunk. Therefore, it is necessary that a configuration of an antireflection film be readjusted every time a finer design rule is applied to the device pattern. That is why the multilayer antireflection film in which the reflectivity of the exposure light is equal to or lower than 0.5% is expected to restrain the standing wave effect.
However, the introduction of the multilayer antireflection film specializing in the decrease in reflectivity cannot avoid a process cost increase caused by increasing the number of film applying processes. Generally, in the antireflection film, not only the antireflection performance but also etching-resistant properties are required when a pattern of the photoresist layer is transferred to the processed layer in an etching process subsequent to a lithography process. Therefore, it is necessary to establish a balance between the lithography process and the etching process.
For example, the exposure process is performed using a film structure in which a lower-layer film is provided between the photoresist layer and the processed layer. The lower-layer film is proven in the etching-resistant properties although the reflectivity is set to about several percent that is not ideal.
Thus, frequently the new multilayer antireflection film specializing in the decrease in reflectivity is hardly introduced.
As described above, currently there is no effective countermeasure against the focal depth loss caused by the presence of the sparse and dense best focus difference and the lowering of the margin of the exposure amount caused by the influence of the standing wave in the photoresist, and the production yield of the most-advanced semiconductor device cannot be enhanced.